The filters of filter cigarettes are generally manufactured from a so-called filter tow made from cellulose acetate. It is removed from a bale of cellulose acetate and formed into a web or a strand, before it is passed to the machine in which the filter plugs are manufactured. The ‘tow’ removed from the bale is highly crimped and is therefore subjected to tensile stress to spread it out. To this end two roller pairs are provided spaced apart, of which that located to the front in the direction of transport is driven with greater speed than that to the rear, in order thereby to create tension.
The roller pairs used until now are mounted with one end on the frame of the machine, one roller consisting of metal and the other comprising a surface layer made from resilient material, for example rubber or the like. Such provisions are disclosed in, amongst others, DE 1 532 142 or DE 2 008 033.
In the known roller pairs the roller located above and consisting of metal is driven, whilst the lower roller is mounted to run with it. To thread the filter tow the lower roller is pivotally mounted about a horizontal axis in the vicinity of its mounting. To actuate the pivoting a linear pneumatic drive is provided.
So that a certain stretching of the tow can be carried out without slipping, the lower roller has to be pressed with relatively high press force. As a result, however, the rubber coating of the lower roller is subjected to not inconsiderable wear and tear.
The object of the invention is to modify a roller pair of the aforementioned type to such an extent that wear and tear is reduced.
According to the invention, the second roller can also be driven by a drive via a second drive shaft and an articulated shaft. According to an embodiment of the invention the second drive shaft is coupled via a gear mechanism to the first drive shaft. Therefore an additional drive is not required.
According to the invention, moreover, the second roller is mounted such that the size of the gap between the rollers can be altered along its length depending on the thickness of the material.
According to the invention, the pressure has to be only so great that the acetate threads can be secured between the roller pairs which are spaced apart, in order to stretch them by a certain proportion. In this manner the wear and tear of the coating of the second roller is markedly reduced.
According to the invention, the second roller is mounted not only so that it can swing away from the first roller but also during operation can carry out limited pivoting or undergo an adjustment parallel to itself, when this is appropriate due to the thickness of the material. The resistance which has to be overcome during such a movement of the second roller is that of the pivot drive which therefore acts upon the second roller in an appropriate manner via a spring medium. This can, for example, occur because the actuation device for its part contains a compressed air cylinder which automatically allows limited pivoting of the roller. Alternatively, a further actuation device can act upon the pivoting of the second roller via a spring medium.
According to a further embodiment of the invention, the second roller is coupled via a universal joint shaft to the second drive shaft. The second drive shaft can, as already mentioned, be the drive shaft of a gear mechanism of which the input shaft represents the motor shaft.
According to a further embodiment of the invention, the second roller is hollow. A drive flange is fastened in the interior which cooperates with a roller bearing of which the inner ring is pivotally mounted about a horizontal axis on a sleeve-shaped bearing component. The articulated shaft is passed through the sleeve-shaped component. The sleeve-shaped component is for its part again pivotally mounted on the frame about a horizontal axis. As a result, on the one hand the bearing component is pivotally mounted and can transmit this movement to the roller. On the other hand the roller is for its part pivotally mounted on the bearing component, so that it can also be adjusted parallel to itself, for the purpose of adapting to the thickness of the filter tow.